The ion electrode method involves placing an ion electrode and a reference electrode in a solution, separated by an ion-selective membrane, and measuring the potential difference between the two electrodes to determine ion concentration. The reference electrode contains an internal solution (KCl) within it. To maintain a constant concentration at the inner electrode and achieve conductivity, the internal solution flows out through the liquid junction into the solution, thereby exhibiting a constant potential and serving as a reference. A potential difference corresponding to the ion concentration difference between the solutions on either side of the ion-selective membrane occurs, and this potential difference can be measured using a reference electrode. An appropriate ion-selective membrane is used depending on the type of ion to be measured.
Schematic diagram of electrodes and ion-selective membrane
Schematic diagram of a potential difference across an ion-selective membrane

